Within the Blohm and Voss shipyard in Hamburg, Germany, there are several large underground bunkers which in their heyday would have protected thousands of workers during the allied air raids. Bismarck was built here but in the war, the shipyard was mostly used for U-boat construction and repair of warships / U-boats.

Notice the pockmarks from the WW2 air raids

Above Ground entrance with bomb resistant roof

Sub-surface entrance

Stairs down to entrance - note flood protection barriers which can be fitted